438 On the Food of Plants, 



must be conducted on or in the earth, we may consider these 

 operations as analogous to digestion : and just as the earth pos- 

 sesses the requisite quahties for digesting and distributing the 

 carbonaceous matter, or the food supplied, it will prove more 

 or less adapted to the support of vegetables. The digestive 

 powers of the earth must depend upon its chemical qualities, 

 and its distributive powers on its mechanical texture. Thus, 

 calcareous earths have great influence in modifying the de- 

 composition and recomposition of animal and vegetable sub- 

 stances ; and the mechanical texture of the soil, as it admits 

 or obstructs an equal and free distribution of water, must 

 also very much influence the growth of vegetables. 



Pursuing our comparisons, then; as we know that the health, 

 vigour, and prolificness of animals depend as much upon the 

 quality and proper digestion of their food as upon the quan- 

 tity, and upon the proper adaptation of their lodging, and the 

 climate which they are doomed to occupy, so we find it to be 

 the same with vegetables : and, as the success of the grazier 

 and breeder depends upon the skill with which the food is 

 selected and administered to his animals, the clean state of 

 their lodgings, and the purity of the air in which they are 

 kept, so must that of the gardener with his plants. It is well 

 known, that if an animal which has been living on a poor and 

 meagre diet is suddenly supplied with an excess of highly 

 stimulating food, the dangerous disorder called a surfeit, and 

 all its consequences, will follow ; and such will always be 

 the case with vegetables : for whenever water containing a 

 large portion of putrefying matter, from whatever source de- 

 rived, stagnates about the roots of a plant, it will produce 

 gum, canker, morbid exudation, blotched and blistered leaves 

 and shoots, fungus, &c. ; and a quantity of putrefying animal 

 matter being placed in contact with the roots of plants, and 

 holding water in a stagnant state, will produce the same effects. 

 It is believed by some, that those diseases are merely local ; 

 but this is a mistake. Local injuries may facilitate and deter- 

 mine the appearance of disease ; but as the same kind of 

 wound which will create inflammation, disease, and death, in 

 one animal, may be inflicted on another without any such 

 injurious consequences, so it is with plants. A plant in a 

 healthy state may be wounded with impunity ; whereas the 

 slightest bruise in one in an unhealthy state will immediately 

 putrefy, and produce a corrosive ulcer. But, whether these 

 comparisons be admitted as just or not, the causes and effects, 

 as explained, are found to he true, by the practical demon- 

 strations of actual and repeated experience and observation. 

 If any persons entertain any doubt of the facts, let them 



